Winter in a Passive House

Submitted by Andrea
on December 30, 2012

We've been living in the house for a little more than four months now, but it seems like much longer than that (in a good way). The long ordeal of planning and construction has faded from our memories, and we're simply enjoying living here. In most respects the house is performing extremely well. The 12,000 BTU heat pump is having no trouble keeping the entire house comfortable. Outdoor temperatures haven't fallen much below 20°F yet (-7°C), so it hasn't really been challenged, but we're not too worried. We left town for a few days last week and turned the heat pump down to 60° (it's normally set to 68), and it never even ran while we were away. The indoor temps ranged from 62-66°, even though outdoor temps stayed below freezing. Our one complaint this winter is that the house has been extremely dry (relative humidity ranging between 20-25%), with our heat recovery ventilator running on low, at 62 CFM. This isn't too surprising, since Ted and I are only two people living in a fairly voluminous house without pets. We don't have any houseplants yet either, but I plan to remedy this soon by setting up our indoor vegetable garden upstairs (that will be a whole other post, hopefully in the near future). For now our solution is to run a humidifier. (I know, so pedestrian!) The main problem is that the humidifier is quite loud, drowning out our whisper-quiet heat pump and HRV. Our long-term fix will be to add plants and see how that affects things, and then maybe get an ERV core for the ventilation system. It's pretty easy to swap cores, apparently, and the ERV will transfer moisture from the outgoing stale air to the incoming fresh air. Naturally, our many geeky onlookers (including Peter Schneider of Efficiency Vermont, who installed all the monitoring equipment) will be curious to see what difference the ERV makes for comfort and energy use.

You may have noticed that this post is called "Winter in a Passive House," and not "Winter in an Almost Passive House." This is because we built a full-fledged, certifiable passive house (pending the actual certification, which we haven't gotten around to yet). We made the decision ages ago, but I never changed the name of the site because I didn't want to jinx things. I'm not so worried now, since we did insanely well on our blower door test (91CFM, which translates to 0.29ACH50). I therefore feel pretty confident about our final PHPP numbers, even if we messed up a thermal bridge calculation or two.

I haven't decided what we should rename the site, so for now I'll just strike out the "Almost" and see where the spirit moves me. Speaking of winter, here are some lovely new snowy pix!

Random Bits

Ordinary houses breathe through leaky joints and poor seals, losing heat and wasting energy. But our house won't leak, so we'll use a heat recovery ventilator (HRV) to admit fresh air and expel stale air, transferring heat from one stream to the other.